internal/lsp: remove module diagnostics from code actions
internal/lsp: remove module diagnostics from code actions

With -mod=readonly, all go.mod diagnostics are covered by go get quick
fixes on import statements, so we don't need to run `go mod tidy` on
save for Go files. The real issue with this bug is the call to
WorkspacePackages, which type checks every package in the workspace.

Fixes golang/go#45092

Change-Id: Ibb82a3e58ec345ebdb67c0cbef5e029dce2d5a30
Reviewed-on: https://go-review.googlesource.com/c/tools/+/303149
Trust: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>
Run-TryBot: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>
gopls-CI: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools